1. Field of the Invention
Embodiments relate to a semiconductor memory device. More particularly, embodiments relate to a high voltage regulator for a non-volatile memory device capable of rapidly and accurately regulating a program voltage.
2. Description of the Related Art
A flash memory is a high-density and non-volatile memory capable of electrically storing data and programming. Data may be freely written and deleted in the flash memory like a RAM. The flash memory may maintain data stored in a chip without power like a ROM. Therefore, flash memories are widely used as memory devices in portable electronic products, e.g., digital cameras, personal digital assistants (PDAs), MP3 players, and the like.
A single level cell (SLC) flash memory is a flash memory storing one bit of data in one memory cell. A multi level cell (MLC) flash memory is a flash memory storing more than 1 bit of data in one memory cell so as to improve packing density.
When 1-bit data is stored in a flash memory, each memory cell may have a threshold voltage that falls within one of two threshold voltage distributions, which correspond to data 1 or data 0. When 2-bit data is stored in a flash memory, each memory cell may have a threshold voltage falling within one of four threshold voltage distributions. When 3-bit data is stored in a flash memory, each memory cell may have a threshold voltage falling within one of eight threshold voltage distributions, and so forth.
In a flash memory including the SLC or the MLC, the data stored in the memory cell may be read by monitoring cell currents when a read operation is performed. The read operation of a SLC flash memory and a MLC flash memory is not described in more detail here because the operation is familiar to those skilled in the art.
High voltage is required for performing programming and verify operations of the flash memory cell. A program voltage for a flash memory device is generated by a high voltage regulator. The high voltage regulator also generates a verify voltage by leveling down the high program voltage to a predetermined level and then leveling up the high program voltage. Using the verify voltage, whether programming has been accurately performed or not may be determined. Generally, the verify voltage is lower than the program voltage.
In a conventional high voltage generator, a node at which the program voltage is sensed and a node at which discharge occurs are different. Therefore, the response difference between the two nodes may result in an overdischarge or an overshooting of the program voltage. Furthermore, the conventional high voltage regulator includes resistors having a relatively large resistance value to reduce an active current. The large resistance value increases the response difference between the two nodes.
The overdischarge and the overshooting of the program voltage are becoming more significant problems as ensuring a program margin of a MLC flash memory becomes more important. The MLC flash memory requires an accurate program and an accurate verify operation.
In addition, the conventional high voltage regulator includes different comparators for detecting a low voltage and a high voltage. Therefore, mismatch between the comparators may cause malfunction of the conventional high voltage regulator.